1. Field of the Invention
The present invention relates to a communication method in a mobile communication network.
2. Description of Related Art
The Internet nowadays performs an important role as the backbone of communication environments. A variety of problems, however, arise in the Internet technologies. One of those problems is concerned with a mobile node (which will hereinafter be abbreviated to MN) in mobile communications. This problem is that an IP address of the mobile node (MN) changes in a location to which the mobile node (MN) is connected, with the result that it is difficult to judge an identity of the mobile node (MN).
Such being the case, Mobile-IP is proposed as a mechanism for assuring connectivity with the mobile node (MN) without changing the IP address of the mobile node (MN).
According to Mobile-IP, a correspondent node (which will hereinafter be abbreviated to CN) forwards a packet to a home address defined as an address on a home link to which the mobile node (MN) is normally attached. On the other hand, a home agent intercepts the forwarded packet and forwards the packet to a care-of address assigned in the visited network of the mobile node (MN) Thus, the mobile node (MN) can receive the packet addressed to the home address.
According to Mobile-IP, however, the communication from the correspondent node (CN) to the mobile node (MN) must be performed via the home agent, and therefore, that the route becomes inefficient poses a problem.
This being the case, Mobile-IPv6 provides a route optimization function of forwarding and receiving the packet a route without through the home agent between the mobile node (MN) and the correspondent node (CN). FIG. 1 shows how the route optimization based on Mobile-IPv6 is set. Note that R1 through R3 represents routers in FIGS. 1 to 4.
Normally, the correspondent node (CN) forwards the packet to the home address defined as the address on the home link of the mobile node (MN) (S101).
On the other hand, the home agent intercepts the forwarded packet addressed to the home address of the mobile node (MN) (S102). Then, the home agent encapsulates the intercepted packet and forwards it to a care-of address assigned in a visited network of the mobile node (MN) (S103).
Then, the mobile node (MN) receives the encapsulated packet. The mobile node (MN), when receiving the forwarded packet, recognizes that the packet comes via the home agent. At this time, it is judged whether a security association between the correspondent node (CN) and the mobile node (MN) is established or not. Herein, if the security association is established, the mobile node (MN) requests the correspondent node (CN) to register a location of the mobile node (MN) and executes a route optimization. Therefore, the mobile node (MN) sends the present care-of address as Binding Update to the correspondent node (CN) (S104). Herein, the information on the location of the mobile node (MN) implies information containing the present care-of address assigned in the visited network of the mobile node (MN).
Further, the state where “the security association is established” is a state in which a database on the mobile node (MN) is stored with a security parameter index (SPI) value coincident with the forwarded packet, and a destination address. The security (authentication of the sender, a safe protection of the data, a protection of reply, etc.) is ensured.
Further, Binding is defined as information retained in a Binding cache on the home agent, namely information about the relationship between the home address of the mobile node (MN) and the care-of address assigned in the visited network of the mobile node (MN). Binding Update implies an update of Binding information.
Then, the correspondent node (CN) receives Binding Update sent from the mobile node (MN), and retains the information about the location of the mobile node (MN) (S105). The correspondent node (CN) acquires the care-of address of the mobile node (MN) from the location information of the mobile node (MN).
From this onwards, the packet to the mobile node (MN) is forwarded to the care-of address (S106). Therefore, the packet addressed to the care-of address, which is forwarded from the correspondent node (CN), can reach the mobile node (MN) via an optimal route between the correspondent node and the mobile node without through the home agent.
As described above, according to Mobile-IPv6, the route optimization can be set. Namely, it is possible to thus perform the communication between the mobile node (MN) and the correspondent node (CN) without through the home agent.
Next, FIG. 2 shows how the route optimization based on Mobile-IPv6 is maintained. The mobile node (MN) sends again Binding Update before an expiration of a predetermined time (which will hereinafter be referred to as a lifetime) set in Binding Update in order to keep the location information sent to the correspondent node (CN). Normally, with this operation, Binding Update continues to be periodically sent to the correspondent node (CN) from the mobile node (MN) (S201).
Then, the correspondent node (CN) receives Binding Update from the mobile node (MN) and updates the location information, thereby keeping the route optimization (S202).
Further, what is proposed as a protocol over Mobile-IPv6 is Hierarchical Mobile-IPv6 for concealing a mobility within a network administered by a mobility anchor point from the home agent by providing a node, i.e., the mobility anchor point (MAP) corresponding to the surrogate home agent in a visited network of the mobile node (MN). FIG. 3 shows how the route optimization based on Hierarchical Mobile-IPv6 is set.
Normally, the correspondent node (CN) forwards the packet to the home address which is an address on the home link of the mobile node (MN) (S301).
On the other hand, the home agent intercepts the packet addressed to the home address of the mobile node (MN) (S302). Then, the home agent encapsulates the intercepted packet and forwards this packet to a regional care-of address as an address under the mobility anchor point of the mobile node (MN) (s303).
Subsequently, the mobility anchor point receives the packet addressed to the regional care-of address, which has been forwarded from the home agent (S304). Thereafter, the mobility anchor point encapsulates the packet addressed to the regional care-of address and forwards this encapsulated packet to an on-link care-of address of the mobile node (MN) (S305).
Ensuingly, the mobile node (MN), when receiving the packet, recognizes that this packet comes via the home address. At this time, it is judged whether the security association between the correspondent node (CN) and the mobile node (MN) is established or not. Herein, if the security association is established, the mobile node (MN) applies the route optimization by registering its location on the correspondent node (CN), and therefore sends Binding Update to the correspondent node (CN) (S306).
On the other hand, the correspondent node (CN) receives Binding Update sent from the mobile node (MN) thereby retaining the information about the location of the mobile node (MN) (S307). At this time, the regional care-of address is registered in an item “care-of address” in the location information. Namely, the correspondent node (CN) can acquire the regional care-of address of the mobile node (MN) from within the location information of the mobile node (MN).
Then, the correspondent node (CN), from this onwards, forwards to the mobile node (MN) the packet to the regional care-of address thereof (S308). Subsequently, the mobility anchor point receives the packet addressed to the regional care-of address from the correspondent node (CN) (S309). Therefore, the packet addressed to the regional care-of address from the correspondent node (CN) can reach the mobility anchor point via an optimal route between the correspondent node (CN) and the mobility anchor point without through the home agent. Subsequently, the mobility anchor point encapsulates the packet addressed to the regional care-of address and forwards this encapsulated packet to the on-link care-of address of the mobile node (MN) (S310).
As described above, according to Hierarchical Mobile-IPv6, the route optimization can be set as based on Mobile-IPv6. That is to say, it is possible to thus perform the communication between the mobile node (MN) and the correspondent node (CN) via the mobility anchor point without through the home agent.
FIG. 4 shows how the route optimization based on Hierarchical Mobile-IPv6 is maintained. The mobile node (MN) sends again Binding Update before the expiration of the predetermined time (lifetime) set in Binding Update in order to keep the location information sent to the correspondent node (CN). Normally, with this operation, Binding Update continues to be periodically sent to the correspondent node (CN) from the mobile node (MN) (S401). Then, the correspondent node (CN) receives Binding Update from the mobile node (MN) and updates the location information (S402), thereby keeping the route optimization.
A start of the route optimization in the prior art described above is triggered by the process that the mobile node (MN) receives the packet from the correspondent node (CN). Accordingly, there might be a case where the packet forwarding route is to be changed in an underway communication from the corresponding node (CN) to the mobile node (MN).
If the route optimization is executed during the communication between the mobile node (MN) and the correspondent node (CN), the communication route is changed, a packet after undergoing the route optimization might arrive at the mobile node (MN) earlier than a packet before undergoing the route optimization. Consequently, a sequence reverse of the packets occurs due to this inconsistency.
Moreover, a retransmission of the packet because of the occurrence of the sequence reverse of the packets leads to an increase in network traffic. As a result, a throughput decreases.
Further, according to the prior art, after executing the route optimization, the mobile node (MN) continues to periodically send, to the correspondent node (CN), Binding Update for updating the location information in order to maintain the route optimization.
Consequently, the continuous communications have been halted after the route optimization has been executed between the mobile node (MN) and the correspondent node (CN), and nevertheless the location information for keeping the route optimization continues to be sent to the correspondent node (CN) from the mobile node (MN). This conduces to an occurrence of an unnecessary traffic in the network. Further, the correspondent node (CN) continues to hold unnecessary pieces of information, resulting in a futility of resources.